ML13080A413
| ML13080A413 | |
| Person / Time | |
|---|---|
| Site: | San Onofre  |
| Issue date: | 03/20/2013 |
| From: | St.Onge R Southern California Edison Co |
| To: | Document Control Desk, Office of Nuclear Reactor Regulation |
| References | |
| TAC ME9727 | |
| Download: ML13080A413 (37) | |
Text
ISOUTHERN CALIFORNIA EDISON An EDISON INTERNATIONAL Company Proprietary Information Withhold from Public Disclosure Richard J. St. Onge Director, Nuclear Regulatory Affairs and Emergency Planning March 20, 2013 10 CFR 50.4 U.S. Nuclear Regulatory Commission ATTN: Document Control Desk Washington, DC 20555-0001
Subject:
References:
Docket No. 50-361 Response to Request for Additional Information (RAIs 38, 40, 41, 57, 59, 60, and 63-67) Regarding Confirmatory Action Letter Response (TAC No. ME 9727)
San Onofre Nuclear Generating Station, Unit 2
- 1. Letter from Mr. Elmo E. Collins (USNRC) to Mr. Peter T. Dietrich (SCE), dated March 27, 2012, Confirmatory Action Letter 4-12-001, San Onofre Nuclear Generating Station, Units 2 and 3, Commitments to Address Steam Generator Tube Degradation
- 2. Letter from Mr. Peter T. Dietrich (SCE) to Mr. Elmo E. Collins (USNRC), dated October 3, 2012, Confirmatory Action Letter - Actions to Address Steam Generator Tube Degradation, San Onofre Nuclear Generating Station, Unit 2
- 3. Email from Mr. James R. Hall (USNRC) to Mr. Ryan Treadway (SCE), dated February 20, 2013, Request for Additional Information (RAIs 38-52) Regarding Response to Confirmatory Action Letter, San Onofre Nuclear Generating Station, Unit 2
- 4. Email from Mr. James R. Hall (USNRC) to Mr. Ryan Treadway (SCE), dated February 21, 2013, Request for Additional Information (RAIs 53-67) Regarding Response to Confirmatory Action Letter, San Onofre Nuclear Generating Station, Unit 2
Dear Sir or Madam,
On March 27, 2012, the Nuclear Regulatory Commission (NRC) issued a Confirmatory Action Letter (CAL) (Reference 1) to Southern California Edison (SCE) describing actions that the NRC and SCE agreed would be completed to address issues identified in the steam generator tubes of San Onofre Nuclear Generating Station (SONGS) Units 2 and 3. In a letter to the NRC dated October 3, 2012 (Reference 2), SCE reported completion of the Unit 2 CAL actions and included a Return to Service Report (RTSR) that provided details of their completion.
Proprietary Information Withhold from Public Disclosure Decontrolled Upon Removal From Enclosure 2 P.O. Box 128 San Clemente, CA 92672
Proprietary Information Withhold from Public Disclosure Document Control Desk March 20, 2013 By emails dated February 20, 2013 (Reference 3) and February 21, 2013 (Reference 4), the NRC issued Requests for Additional Information (RAIs) regarding the CAL response. of this letter provides the response to RAIs 38, 40, 41, 57, 59, 60, and 63-67. of this submittal contains proprietary information. SCE requests that this proprietary enclosure be withheld from public disclosure in accordance with 10 CFR 2.390(a)(4). provides notarized affidavits from MHI, which sets forth the basis on which the information in Enclosure 2 may be withheld from public disclosure by the NRC and addresses with specificity the considerations listed by paragraph (b)(4) of 10 CFR 2.390. Proprietary information identified in Enclosure 3 was extracted from proprietary MHI documents L5-04GA564, L5-04GA567 and L5-04GA585 which are addressed in the affidavits. Enclosure 3 provides the non-proprietary version of Enclosure 2.
There are no new regulatory commitments contained in this letter. If you have any questions or require additional information, please call me at (949) 368-6240.
Sincerely,
Enclosures:
- 1. Notarized Affidavit
- 2. Response to RAIs 38, 40, 41, 57, 59, 60, and 63-67 (Proprietary)
- 3. Response to RAIs 38, 40, 41, 57, 59, 60, and 63-67 (Non-Proprietary) cc:
E. E. Collins, Regional Administrator, NRC Region IV J. R. Hall, NRC Project Manager, SONGS Units 2 and 3 G. G. Warnick, NRC Senior Resident Inspector, SONGS Units 2 and 3 R. E. Lantz, Branch Chief, Division of Reactor Projects, NRC Region IV Proprietary Information Withhold from Public Disclosure Decontrolled Upon Removal From Enclosure 2
ENCLOSURE 1 Notarized Affidavits
MITSUBISHI HEAVY INDUSTRIES, LTD.
AFFIDAVIT I, Jinichi Miyaguchi, state as follows:
- 1. I am Director, Nuclear Plant Component Designing Department, of Mitsubishi Heavy Industries, Ltd. ("MHI"), and have been delegated the function of reviewing the referenced MHI technical documentation to determine whether it contains information that should be withheld from public disclosure pursuant to 10 C.F.R. § 2.390 (a)(4) as trade secrets and commercial or financial information that is privileged or confidential.
- 2. In accordance with my responsibilities, I have determined that the following MHI documents and drawings contain MHI proprietary information that should be withheld from public disclosure pursuant to 10 C.F.R. § 2.390 (a)(4). The drawings in their entirety are proprietary and those pages of the documents containing proprietary information have been bracketed with an open and closed bracket as shown here "[ ]" / and should be withheld from public disclosure.
MHI documents and drawings Document: L5-04GA561, L5-04GA564, L5-04GA571, L5-04GA585, L5-04GA591 Drawings: L5-04FU101 thru 108
- 3. The information identified as proprietary in the enclosed document has in the past been, and will continue to be, held in confidence by MHI and its disclosure outside the company is limited to regulatory bodies, customers and potential customers, and their agents, suppliers, and licensees, and others with a legitimate need for the information, and is always subject to suitable measures to protect it from unauthorized use or disclosure.
- 4.
The basis for holding the referenced information confidential is that it describes unique design, manufacturing, experimental and investigative information developed by MHI and not used in the exact form by any of MHI's competitors.
This information was developed at significant cost to MHI, since it is the result of an intensive MHI effort.
- 5. The referenced information was furnished to the Nuclear Regulatory Commission
("NRC") in confidence and solely for the purpose of information to the NRC staff.
- 6. The referenced information is not available in public sources and could not be gathered readily from other publicly available information.
Other than through the provisions in paragraph 3 above, MHI knows of no way the information could be lawfully acquired by organizations or individuals outside of MHI.
- 7.
Public disclosure of the referenced information would assist competitors of MHI in their design and manufacture of nuclear plant components without incurring the costs or risks associated with the design and the manufacture of the subject component.
Therefore, disclosure of the information contained in the referenced document would have the following negative impacts on the competitive position of MHI in the U.S. and world nuclear markets:
A.
Loss of competitive advantage due to the costs associated with development of technologies relating to the component design, manufacture and examination.
Providing public access to such information permits competitors to duplicate or mimic the methodology without incurring the associated costs.
B.
Loss of competitive advantage of MHI's ability to supply replacement or new heavy components such as steam generators.
I declare under penalty of perjury that the foregoing affidavit and the matters stated therein are true and correct to the best of my knowledge, information and belief.
Executed on this 2 dayof,qJ U
-2012.
Jlt c)A y(I AAC rA-,
Jinichi Miyaguchi, Director-Nuclear Plant Component Designing Department Mitsubishi Heavy Industries, LTD 220,
A i1,1 -2 I2 Sworn to and subscribed Before me this Q
day of A U 5t, 2012 Notary Public My Commission Expires
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Registered Number 2 2 0 Date
-2.2012 NOTARIAL CERTIFICATE This is to certify that JINICHI MIYAGUCHI, Director-Nuclear Plant Component Designing Department MITSUBISHI HEAVY INDUSTRIES, LTD has affixed his signature in my very presence to the attached document.
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MASAHIKO KUBOTA Notary 44 Akashimachi, Chuo-Ku, Kobe, Japan Kobe District Legal Affairs Bureau
(
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MITSUBISHI HEAVY INDUSTRIES, LTD.
AFFIDAVIT I, Jinichi Miyaguchi, state as follows:
- 1. I am Director, Nuclear Plant Component Designing Department, of Mitsubishi Heavy Industries, Ltd. ("MHI"), and have been delegated the function of reviewing the referenced documentations to determine whether they contain MHI's information that should be withheld from public disclosure pursuant to 10 C.F.R. § 2.390 (a)(4) as trade secrets and commercial or financial information that is privileged or confidential.
- 2. In accordance with my responsibilities, I have reviewed the following documentations and have determined that they contain MHI proprietary information that should be withheld from public disclosure. Those pages containing proprietary information have been bracketed with an open and closed bracket as shown here "[ I" / and should be withheld from public disclosure pursuant to 10 C.F.R. § 2.390 (a)(4).
MHI's documents
- L5-04GA567 Evaluation of Stability Ratio for Return to Service
- L5-04GA585 Analytical Evaluations for Operational Assessment SCE's documents
- 10CFR50.59 Evaluation, Screening NECP 800175663 Steam Generator Replacement Mstr ECP U2
- 10CFR50.59 Evaluation, Screening NECP 800175664 Steam Generator Replacement Mstr ECP U3
- 3. The information identified as proprietary in the documents have in the past been, and will continue to be, held in confidence by MHI and its disclosure outside the company is limited to regulatory bodies, customers and potential customers, and their agents, suppliers, and licensees, and others with a legitimate need for the information, and is always subject to suitable measures to protect it from unauthorized use or disclosure.
- 4.
The basis for holding the referenced information confidential is that they describe unique design, manufacturing, experimental and investigative information developed by MHI and not used in the exact form by any of MHI's competitors. This information was developed at significant cost to MHI, since it is the result of an intensive MHI effort.
- 5. The referenced information was furnished to the Nuclear Regulatory Commission
("NRC") in confidence and solely for the purpose of information to the NRC staff.
- 6. The referenced information is not available in public sources and could not be gathered readily from other publicly available information.
Other than through the provisions in paragraph 3 above, MHI knows of no way the information could be lawfully acquired by organizations or individuals outside of MHI.
- 7.
Public disclosure of the referenced information would assist competitors of MHI in their design and manufacture of nuclear plant components without incurring the costs or risks associated with the design and the manufacture of the subject component. Therefore, disclosure of the information contained in the referenced documents would have the following negative impacts on the competitive position of MHI in the U.S. and world nuclear markets:
A. Loss of competitive advantage due to the costs associated with development of technologies relating to the component design, manufacture and examination.
Providing public access to such information permits competitors to duplicate or mimic the methodology without incurring the associated costs.
B. Loss of competitive advantage of MHI's ability to supply replacement or new heavy components such as steam generators.
I declare under penalty of perjury that the foregoing affidavit and the matters stated therein are true and correct to the best of my knowledge, information and belief.
Executed on this
/1 day of /eb-0-'Y
,2013.
Jinichi Miyaguchi, Director-Nuclear Plant Component Designing Department Mitsubishi Heavy Industries, LTD Sworn to and subscribed 31 Before me this - I day of F-4 ra a/,
2013 FEB 1 8, 2013 Notary Public
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Registered Number 3 1 Date FEB.18.2013 NOTARIAL CERTIFICATE This is to certify that JINICHI MIYAGUCHI, Director-Nuclear Plant Component Designing Department MITSUBISHI HEAVY INDUSTRIES, LTD has affixed his signature in my very presence to the attached document.
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'N 12 zILdIv-4 MASAHIKO KUBOTA Notary 44 Akashimachi, Chuo-Ku, Kobe, Japan Kobe District Legal Affairs Bureau
ENCLOSURE 3 SOUTHERN CALIFORNIA EDISON RESPONSE TO REQUEST FOR ADDITIONAL INFORMATION REGARDING RESPONSE TO CONFIRMATORY ACTION LETTER DOCKET NO. 50-361 TAC NO. ME 9727 Response to RAI's 38, 40, 41, 57, 59, 60, and 63 through 67 (NON-PROPRIETARY)
SUBJECT PAGE
RAI 38
2
RAI 40
3 RAI41 5
RAI 57
8 RAI 59 & 67 10 RAI60 13 RA163 16 RAI 64, 65 & 66 20
RAI 38
In Reference 1, p. 8-3 (308 of 474), Section 3.2), "Loading conditions," please explain how ATHOS output is being converted to hydrodynamic pressure. The NRC staff is not aware that this quantity is a direct output of the ATHOS code. Please show a derivation of this parameter, explain how it is computed for the purposes of data reduction and display, and explain its technical significance.
RESPONSE
Note: Request for Additional Information (RAI) Reference 1 is "Tube Wear of Unit-3 RSG - Technical Evaluation Report," MHI Document No. L5-04GA564, Revision 9.
Conversion of ATHOS Output Hydrodynamic pressure is not a direct output of ATHOS. The hydrodynamic pressure in the out-of-plane direction on each tube in the ABAQUS model discussed in Section 3.2 of Reference 1 is calculated by the following equation:
1 Where:
P,: hydrodynamic pressure in the out-of-plane direction at a given location along the tube p: fluid mixture density (ATHOS output) v: fluid gap velocity in the out-of-plane direction (ATHOS output)
Computation for Modeling Purposes The hydrodynamic force (drag force) on a tube is calculated from hydrodynamic pressure as follows:
F = Pv x Cd x D Where:
F: hydrodynamic force per unit tube length at a given location along the tube Pv: hydrodynamic pressure at a given location along the tube Cd: drag coefficient D: tube diameter Hydrodynamic force is applied to each tube element in the contact force finite-element model as a distributed load. The ATHOS results are mapped to the corresponding elements in the bundle analysis.
Explanation of Significance The minor effect of hydrodynamic forces on tube bundle deformation is displayed in the Appendix 8 figures of RAI Reference 1. The technical significance of the hydrodynamic pressure is discussed in the response to RAI 27.
Page 2 of 24
RAI 40
In Reference 2, p. 40, it is stated that "...plugged tubes are assumed to be in wet condition despite the void fraction." Please explain why this assumption is used, and provide information to justify that it is appropriate (i.e., valid, conservative, or insignificant) for the purposes of the relevant analyses.
RESPONSE
Note: RAI Reference 2 is "Evaluation of Stability Ratio for Return to Service," MHI Document No. L5-04GA567, Revision 6.
Use of wetted condition assumption for plugged tubes The assumption of wet condition for plugged tubes is used to apply the appropriate correlations of structural and squeeze film damping. Section 7.1.1.1 of RAI Reference 2 presents different correlations for structural damping depending on whether the tube is in liquid or in gas. Stability ratio calculations performed for plugged tubes use the liquid correlation to evaluate structural damping ratio.
The squeeze film damping ratio correlation is dependent on the number of anti-vibration bar (AVB) support points. For in-service tubes this correlation was modified to only account for the number of wetted AVB support points. For plugged tubes, this modification is not necessary and the original correlation that accounts for all AVB support points was used.
Explain why this assumption is used In two-phase flow at high void fraction, liquid droplets are entrained in the vapor flow. The droplets impinge on the tubes and structures in the bundle. Liquid film flow occurs on the tubes and structures because the transported droplets and mist spread due to the shear stress on the liquid surface from the two-phase flow. Plugged tubes have no heat flux and their outside surface remains wetted.
Provide information to justify that the assumption is appropriate Further investigation of the open literature supports the assumption. Experimental measurements of local liquid film thickness obtained from Reference R1 (citation below),
indicate that the film maintains a minimum finite thickness value under a range of flow and heat flux conditions in annular two-phase vertical flow. Film flow rate and thickness measurements up to 90% exit steam quality were also reported in Reference R2 (citation below), and those tests demonstrate the existence of a thin liquid film in this high-quality vertical steam/water flow.
At 70% power, the ATHOS model for the SONGS replacement steam generator shows that the maximum void fraction in the tube bundle is [
], and maximum steam quality is [ ]. At this void fraction, there is a continuous liquid film on all surfaces as described in Attachment 2 of RAI Reference 2 (pg. 111). All tube-to-AVB intersections of both plugged and in-service tubes are subject to wet conditions at 70% power.
Page 3 of 24
References R1 Okawa T., Goto T. and Yamagoe Y., "Liquid film behavior in annular two-phase flow under flow oscillation conditions," International Journal of Heat and Mass Transfer 53 (2010) 962-971.
R2 W~irtz J., "An experimental and theoretical investigation of annular steam-water flow in tubes and annuli at 30 to 90 bar," Technical Report No. 372, Riso National Laboratory (1978).
Page 4 of 24
RAI 41
Reference 2, p. 61 and 63, Tables 8.1.1-1 and 8.1.2-1. The data in Table 8.1.1-1 are based on an assumption that all supports are active, whereas the data in Table 8.1.2-1 are based on an assumption that 1 support is inactive. The NRC staff observed that [
]. Please explain the significant causes of the difference in two-phase damping between these two cases. [Proprietary]
RESPONSE
Note: RAI Reference 2 is "Evaluation of Stability Ratio for Return to Service," MHI Document No. L5-04GA567, Revision 6.
The two cases have different two-phase damping ratios because two-phase damping is a function of effective homogeneous void fraction. The effective homogeneous void fraction is the mode-shape-weighted average of the homogeneous void fraction distribution. The two-phase damping is different for the same thermal-hydraulic conditions because the two cases have different vibration mode shapes.
The two-phase damping ratio is correlated by the following equations (Equations 11 to 15 (P.36) of RAI Reference 2).
,P 4 (PD~(l P
+D 0 /D) cT[
- (D, / D,)2J 8f40 for
< 40%
I for 40%<fl_<70%
I -(!
-70)/30 for 6 >70%
De= r+I P/Do>P mo = m, + mp + mt m
)
0 _
(D, IDo)2 +1 4
L (De IDo),1 2
- Where,
ýTP
- Two-phase damping ratio Effective Homogeneous void fraction Do
- Tube outside diameter De
- Tube equivalent outside diameter P
- Tube pitch Po
- Density of secondary mixture flow (Calculated by ATHOS) p I
- Density of secondary liquid flow MO
- Average tube mass per unit length mv
- Virtual added mass per unit length Page 5 of 24
mp Mass of primary coolant in tube per unit length Mt
- Mass of tube metal per unit length The effective homogeneous void fraction is the mode-shape-weighted average calculated from the following equation, integrated over the length of the tube (Equation 10 (P.36) of RAI Reference 2):
f6= J02dX
- Where, P3
- Homogeneous void fraction 0
- Vibration mode x
Tube axis Page 6 of 24
The following figures show mode shapes for two support conditions:
/
/!
/
(a) All supports are active (b) One support is inactive The highest calculated stability ratio is obtained when the inactive support location coincides with the region of highest void fraction. This region has the strongest mode-shape weighting for the effective homogeneous void fraction calculation with one inactive support. The effective homogeneous void fractions (/f ) for each tube and support case are shown in the table below.
Using the equations shown above, the difference in effective homogeneous void fraction results in approximately a three times greater two-phase damping ratio for the case with all active supports than the case with one inactive support.
All Supports Active One Support Inactive Tube RAI Ref 2 Table 8.1.1-1)
(RAI Ref 2 Table 8.1.2-1)
Row Col (T)
JTP y, %
f(l)
ýTP 80 70 80 80o 100 70 100(*)
80(*)
120 70 120 80 95(*)
85(*)
125 85 138, 84 Note (*): Plugged tube with Type J stabilizer Page 7 of 24
RAI 57
In Reference 3, Appendix 9, Table 6.2-1, why is tube support plate (TSP) hole mis-location not included in the table headings? If not accounted for in the analysis, explain why the approach is conservative. If used in the analysis, provide an updated table that includes the TSP hole mis-location parameter.
RESPONSE
Note: RAI Reference 3 is "Tube Wear of Unit-3 RSG - Technical Evaluation Report," MHI Document No. L5-04GA564, Revision 9.
The TSP hole mis-location (pitch variation) was inadvertently omitted from Table 6.2-1, but was accounted for in the contact force analysis. Table 6.2-1 was updated by adding the TSP Hole Position, and is provided as requested.
Page 8 of 24
Updated Table 6.2-1 Measurement results of the dimensions Unit: mm (mils)
AVB thickness change from Standard deviation a Unit nominal Tube AVB thickness change Tube A
2 AVB Tube TSP Hole 6A ovality from nominal UA AVB twist Flatness*
Sr govality BTA 3
Flatness position BendingStraight Bending Straight po rtn O'S Bar portion Bar GBA
[ ] [ ]
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Go/No-Go/No-go Note Measured Measured Measured Measured Measured Measured Go/No-go checked go checked Sampled checked Note) *1:AVB thickness of bending portion is assumed based on the fact obtained by the AVB pressing test results (See -1 for details), which indicated that AVB nose thicknesses of Unit-2 SGs are larger than Unit-3 SGs due to the difference of AVB pressing load ([ ] for Unit-2 SGs and [
] for Unit-3 SGs) and the side wide AVBs of Unit-2 are thinner than other types of AVBs.
- 2:AVB twist probability distributions are assumed based on the AVB pressing test results (See Attachment 9-1 for details). The probability distribution multiplied by the factor of each AVB type, shown in this table, is assumed.
- 3: AVB Flatness is judged as 0, because AVB flatness is assumed macro distortion.
Page 9 of 24
RAI 59
In Reference 3, Appendix 9, Attachment 9-1; define the statistical distributions which were actually sampled for Unit 2 and Unit 3. What is the technical justification for the assumed distributions compared to the actual distribution of the data?
RAI 67
Reference 3, Appendix 9, Attachment 9-3; describe in detail any "tuning" of the contact force model that was performed to replicate the ding signals observed during pre-service inspection.
RESPONSE
Note: RAI Reference 3 is "Tube Wear of Unit-3 RSG - Technical Evaluation Report," MHI Document No. L5-04GA564, Revision 9.
Three probability distribution functions (PDF) for Side Narrow and Center Narrow AVBs for Unit 2 and Center Narrow for Unit 3 were created from actual distributions of data. (See Figure 1 for Side Narrow and Center Narrow AVBs locations). These three measured PDFs were multiplied by amplification ("tuning") factors in order to produce eight input PDFs, one for each AVB type in each unit. The amplification factors were adjusted to replicate the ding signals in the pre-service inspections. Figures 2 and 3 show the measured PDFs, amplification factors and the resulting PDFs used as inputs to the contact force models. The resulting input PDFs were the statistical distributions which were actually sampled for Unit 2 and Unit 3.
The following explanation provides details for the input PDFs of each AVB type (Center Narrow, Center Wide, Side Narrow and Side Wide). Unit 2 Center Wide AVB and Side Wide AVB input PDFs were generated from Center Narrow [ ] ton press measured PDF. The bending angles of the Center Wide and Side Wide AVBs are closer to the Center Narrow AVB bending angle than that of the Side Narrow AVB. For Unit 3, the Center Narrow [ ] ton press measured PDF was used to generate all Unit 3 input PDFs. Using the Center Narrow AVB only for Unit 3 is reasonable because [ ] ton press reduces AVB twist scatter such that the twist distribution due to AVB bending angle is negligible.
SCenter NarrowAV Center Wide Side Narrow AVi Side Narrow AVB Side Wide AVF e1A**VBCofguaWidetion Figure 1 - AVB Configuration Page 10 of 24
Figure 2 - Measured test data and input PDFs for Unit 2 Page 11 of 24
Figure 3 - Measured test data and input PDFs for Unit 3 Page 12 of 24
RAI 60
In Reference 3, Appendix 9, Figures 7.2-3 and 7.2-5 apply to Unit 3. Please provide similar figures for Unit 2.
RESPONSE
Note: RAI Reference 3 is "Tube Wear of Unit-3 RSG - Technical Evaluation Report," MHI Document No. L5-04GA564, Revision 9.
Figures 7.2-3 and 7.2-5 were updated to include Unit 2 data and to correct Unit 3 data. The revised figures are provided below.
Page 13 of 24
Unit-2 Unit-3 Figure 7.2-3 Displacements at each AVB contact point of Row1O0 tubes in Case 1 & 2 Page 14 of 24
Figure 7.2-5 Inverse of average gap at each AVB point Row100 tubes in Case 1 and 2 Page 15 of 24
RAI 63
In Reference 3, Page 66, the last sentence on this page states, "Therefore, the difference of the contact forces between Unit-2 and Unit-3 is caused by the difference of the manufacturing dimensional tolerances other than the outer-most tube-to-AVB gaps." Explain the basis for this conclusion in light of the omission of the measured tube-to-AVB gaps at the outer tubes as a boundary condition in the contact force model described in Appendix 9 of Reference 3.
RESPONSE
Note: RAI Reference 3 is "Tube Wear of Unit-3 RSG - Technical Evaluation Report," MHI Document No. L5-04GA564, Revision 9.
It is important to note that the outermost tube rows did not exhibit instability in either the tube stability analysis or in the actual steam generators.
The following figure shows the distribution of the as-measured outermost tube-to-AVB radial gaps.
It is noted that the outer-most gaps were measured by a feeler gauge. The vast majority of gaps were measured at less than [ ] mils and there was no significant difference between the measurements in Unit 2 and Unit 3.
Page 16 of 24
The randomly selected input gaps for the entire tube bundle in the contact force model (including outermost tubes) varied from [ ] to [ ] mils as shown in the following two figures. The mean value was approximately [ ] mils and standard deviation was [ ] mils.
.. m Distribution of input radial gaps As these figures show, the input gaps to the contact force model bound the as-measured outermost tube-to-AVB gaps.
The outermost tube rows did not exhibit instability in either the probability of fluid elastic instability calculation or in the actual steam generator.
Page 17 of 24
Because an AVB does not have sufficient stiffness, the contact forces for the interior rows are not affected by the variation of the outermost tube-to-AVB gap. Calculations were performed by rerunning the contact force models for both units with redistributed tube-to-AVB gaps at the outermost rows. As shown in the following figures, the average contact forces near the outer-most row slightly changed, but the contact forces in the inside rows did not.
Original (from Figure 7.2-1)
Redistributed Distributions of the average contact forces of each row in Unit 2 Page 18 of 24
Original (from Figure 7.2-2)
Redistributed Distributions of the average contact forces of each row in Unit 3 Page 19 of 24
RAI 64
In Reference 3, Appendix 9, page 9-6 (355 of 474), it is stated, "Especially for AVB twist, AVB twist factor in consideration of torsion stiffness is defined as a decrease function of distance from AVB bending peak, because the more contact points leave from AVB nose, the less AVB torsion stiffness is." Please clarify the meaning of this sentence by answering the following questions: What is the "AVB twist factor?" What is meant by "AVB twist factor in consideration of torsion stiffness?" What parameter is decreasing as a function of distance from the AVB nose, AVB twist or AVB torsional stiffness? Why does torsional stiffness vary as function of distance from the AVB nose? Describe the specific variation of torsional stiffness with distance from nose function that was used in the analysis. How was this variation determined?
RAI 65
In Reference 3, Appendix 9, Figure 6.2.2 shows AVB twist factor as a function of distance from AVB nose tip. Is this the function that was used in the contact force analysis? For all AVBs? If not, what twist factor functions were used for the other AVBs? How were these twist factor functions determined? Explain the relationship between twist factors shown in this figure versus those shown in Table 6.2-1.
RAI 66
In Reference 3, Appendix 9, page 9-6 (355 of 474) it is also stated, "In AVB nose area, the factor is always 1, because increased twist from nose tip and decreased stiffness from nose tip cancel each other." Please provide a detailed clarification of this sentence. The staff further notes that "twist" and "stiffness" have different units. How can they cancel each other out?
RESPONSE
Note: RAI Reference 3 is "Tube Wear of Unit-3 RSG - Technical Evaluation Report," MHI Document No. L5-04GA564, Revision 9.
RAIs 64 - 66 are related to AVB twist factors.
What is the "AVB twist factor?"
AVB twist factor is defined as:
~ki+kj Where:
k, is the AVB out of plane spring stiffness due to twist k2 is the radial tube compression stiffness.
Page 20 of 24
What is meant by "AVB twist factor in consideration of torsion stiffness?
AVB spring stiffness k, is derived from beam torsion theory. In the case where a moment acts upon a beam, the relation of moment, Mt, and torsion angle, et, is expressed as follows:
MX moment CL Mit moment Where:
G: shear modulus of elasticity Ip: polar moment of inertia of area Considering that this beam represents an AVB, the relation of contact force, F, and AVB displacement due to twist, a, is expressed as follows:
F F
Mt GIP (bD2 +(hJ 2 ý(bD ~(ýD *L GIP a
(because a << b)
( b 2
( h b
S GIp
,a
--I k1a k1=
- 2* +2
.b F=R
- - - --J i h: thickness AVB cross section quantity inside red box and,
,a8 What parameter is decreasing as a function of distance from the AVB nose, AVB twist or AVB torsional stiffness? Why does torsional stiffness vary as function of distance from the AVB nose?
AVB spring stiffness due to twist, kl, decreases as a function of distance because it is inversely proportional to distance, L, from AVB nose tip. AVB twist factor is also a function of distance from the AVB nose tip.
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Describe the specific variation of torsional stiffness with distance from nose function that was used in the analysis. How was this variation determined?
The response to the previous question explained the variation of torsional stiffness with distance from the AVB nose tip. AVB twist factor, which is related to torsional stiffness, was the input parameter used in the contact force analysis. AVB twist factor decreases as a function of distance from the AVB nose tip. Since the AVB is fixed at the retaining bar, the AVB twist factor is also a function of distance from the retaining bar. The variation was determined analytically and the resulting relationship is plotted in Figure 6.2-2 from RAI Reference 3, Appendix 9.
AVB nose Figure 6.2-2 from RAI Reference 3, Appendix 9 Is this the function that was used in the contact force analysis? For all AVBs? If not, what twist factor functions were used for the other AVBs? How were these twist factor functions determined?
Yes, this function was used in the contact force analysis. The function was used for all AVBs.
The AVB twist factor depends on AVB length. Three typical AVB twist factors are shown in the following figure. As described above, the twist factor functions were determined analytically, using strength of materials formulas.
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m.... *r Typical AVB twist factors Explain the relationship between twist factors shown in this figure [6.2-2] versus those shown in Table 6.2-1.
Figure 6.2-2 shows the typical distribution of AVB twist factor along AVB length. Table 6.2-1 shows AVB twist amplification constants used for "tuning" the contact force model to replicate the ding signals observed during pre-service inspection. AVB twist amplification constants are further discussed in the response to RAIs 59 and 67.
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"In AVB nose area, the factor is always 1, because increased twist from nose tip and decreased stiffness from nose tip cancel each other." Please provide a detailed clarification of this sentence. The staff further notes that "twist" and "stiffness" have different units. How can they cancel each other out?
AVB twist is generated by bending an AVB straight bar during manufacturing as shown in the following figure.
bending bending Twisted Twisted AVB Bending Process (Twist Generation)
AVB twist at the AVB nose tip (centerline of AVB) is taken as a reference point and the AVB twist factor is considered to be 1.0 at the nose tip. The bending process increases the AVB twist to a maximum at the start of the straight section. AVB torsional stiffness, which is inversely proportional to AVB length, decreases from the AVB nose tip to the start of the straight section.
Contact force increases due to AVB twist but decreases due to AVB torsional stiffness. The increase and decrease approximately cancel through the nose section. To reflect this, the contact force model used a constant AVB twist factor of 1.0 in the AVB nose section.
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